Polylactide Matrix Research Articles

The wettability, mechanical and antimicrobial properties of polylactide/montmorillonite nanocomposite films.

The aim of this study was to evaluate the effect of the not activated (unmodified) montmorillonite (MMT) filler on the antibacterial properties of polymer nanocomposites with a biodegradable polylactide (PLA) matrix. The subject of research was selected to verify the reports on the lack of antibacterial properties of unmodified montmorillonite in nanocomposites and to investigate the potential conditions of their manufacturing which are decisive for the resulting properties. Evaluation of antibacterial and mechanical properties of both the starting materials and the obtained nanocomposites filled with layered silicates as well as the wettability of the materials, measured by a sitting drop method was made on samples in the form of a film. The results show that the surface wettability of the polymer nanocomposites did not exhibit significant change compared to the film of neat PLA. However, a significant improvement in the mechanical and antimicrobial properties of the nanocomposite films obtained in a specific solvent casting process of the nanocomposite preceded by exfoliation of the film in an ultrasonic homogenizer was demonstrated. The antibacterial activity against Gram-positive bacteria Staphylococcus aureus and Enterococcus faecalis was also observed, and, moreover, the montmorillonite-containing films revealed a zone of inhibition of bacterial growth when tested against the lactosepositive bacteria of the Enterobacteriaceae family, which are present in the waste water. The advantageous properties of the obtained PLA/MMT nanocomposites suggest that the unmodified montmorillonite may be potentially used as filler for polymer films in the packaging industry.

Crystallinity and mechanical properties of polylactide/ether‐amide copolymer blends

ABSTRACTThe present study focuses on the improvement of impact properties and particularly on the interaction between crystallinity development and mechanical properties of impact modified polylactide (PLA). The PLA was toughened by the addition of a random linear ether‐amide copolymer (PEBAX 3533™). A random copolymer of ethylene, methyl‐acrylate, and glycidyl‐methacrylate (LOTADER AX8900™) was also used to reactively compatibilize the ether‐amide copolymer with the PLA matrix. Melt rheology of the blends was investigated in small amplitude oscillatory shear and showed that the impact modifier could significantly influence the viscoelastic response of the material. The Izod impact resistance and tensile properties were measured using standard testing protocols. The blend morphology was also examined using scanning electron microscopy on cryofractured and microtomed surfaces, while the crystalline morphology was assessed by optical microscopy. A sub‐micron dispersion of the impact modifier was achieved in the presence of the reactive compatibilizer. Significantly improved impact strength was found with 10 wt % impact modifier. High crystallinity samples showed the highest impact strength with values reaching 68 kJ/m2, hence a 20‐fold improvement with respect to the neat PLA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44677.

Highly toughened polylactide/epoxidized poly(styrene-b-butadiene-b-styrene) blends with excellent tensile performance

Polylactide (PLA) has inherent shortcomings which limit its widespread application: brittleness, low elongation and low melt strength. In this paper, these problems were addressed through melt blending of PLA with an epoxidized thermoplastic elastomer, epoxidized poly(styrene-b-butadiene-b-styrene) (ESBS). ESBS with different epoxidation degree were prepared by an in-situ peroxy-formic acid method. The Tg of ESBS increased while the flexibility decreased with increasing epoxidation degree. The impact strength improved from 29.9J/m for pure PLA to 891.0J/m for the blend with 30wt% ESBS35.8%, meanwhile, the elongation at break increased from 3.5% to 253.8%. In-situ compatibilization of these immiscible blends was achieved via melt blending of PLA with ESBS that led to the formation of graft copolymer architecture at the interface. The compatibility between PLA matrix and ESBS phase increased gradually while the notched impact strength increased firstly and then decreased with increasing epoxidation degree of ESBS. The morphology of PLA/ESBS blends played an important role in notched impact strength and could be controlled by adjusting the epoxidation degree of ESBS. Rheological tests showed a drastic enhancement of melt viscosities for PLA/ESBS blends in oscillatory experiments. Therefore, the mechanical properties could be easily tailored by the epoxidation degree of ESBS.

Improvement in toughness of polylactide/poly(butylene adipate-co-terephthalate) blend by adding nitrile rubber

This paper describes the preparation and characterization of the effects of polylactide (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and nitrile rubber (NBR) blends. First, a commercial PLA/PBAT blend was characterized by using the Fourier transform infrared spectroscopy and thermal gravimetric analysis. The results show that commercial blend is composed by ~70 wt% of PLA and 30 wt% of PBAT. The PLA/PBAT/NBR blends and also a reference of PLA/PBAT blend were processed by extrusion and compression molding. Then, all compositions were evaluated by their toughness and the thermal behaviors. Special attention was given to the morphology evaluated by scanning electron microscope. The result showed PLA presented in all compositions suffered thermo-mechanical degradation. However, a significant improvement in the toughness was observed for all compositions produced with NBR. That fact was proved by both Izod impact test and the morphology analyses. Additionally, the morphology comparison among the blends also shows that the addition of NBR helps to reduce the size of the PBAT domains in the PLA matrix.

Thermal, structural and mechanical analysis of polymer/clay nanocomposites with controlled degradation

The aim of this study was to investigate the influence of the addition of smectite clay fillers to a polylactide matrix on the physical properties of the nanocomposites thus created, studied during the degradation process. A small amount of nanofiller (3–10 mass %) was used, and the clay was additionally modified with organic ammonium salt for better compatibility with the polymer matrix. Crystallisation, glass transition and melting temperature of the nanocomposites were investigated, and the resulting thermal, structural and mechanical properties were compared to those of a neat polylactide. The degradation process of the materials was examined during immersion in distilled water at 80 °C for 60 days using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Macroscopic changes were monitored and mechanical properties tested prior to degradation to evaluate the ability of the modified clay filler to reinforce the polymer and enhance elastic modulus, mechanical strength and Brinell hardness. The influence of the modified smectite filler on the thermal, mechanical and structural properties of the nanocomposites during degradation and its dependence on filler content were discussed and confirmed in the study. It was found that the addition of 3 mass% of the clay filler provides an increase of nearly 20 % in tensile strength, with improved stiffness. It was also found that the addition of organically modified clay to the polymer matrix significantly changes the hydrolytic degradation mechanisms of the polylactide, the crystallinity of the polymer and its degradation rate, depending on the amount of the filler.

Reactive Compatibilization of Biobased Polyurethane Prepolymer Toughening Polylactide Prepared by Melt Blending

Polylactide (PLA) is a major biodegradable polymer, which has received extensive interests over the past decades and holds great potential to replace several petroleum-based polymeric materials. Nevertheless, the inherent brittleness and low impact strength have restricted its invasion to niche markets. In this paper, the authors demonstrate that the entirely bio-sourced blends, namely PLA and castor oil-based polyurethane prepolymer (COPUP), were first melt-compounded in an effort to prepare novel biodegradable materials with an excellent balance of properties. NCO-terminated COPUP was successfully synthesized and subsequently mixed with variable concentration of PLA matrix using melt-compounded by twin-screw extrusion technique. The miscibility, phase morphology, mechanical properties, and thermal resistance of the blends were investigated. During FTIR analysis, it suggests that the interfacial compatibilization between COPUP and PLA phase occurred by the reaction of –NCO group of MDI with terminal hydroxyl group of PLA. DMA analysis showed that COPUP and PLA showed some limited miscibility with shifted glass transition temperature. The morphologies of fracture surface showed a brittle-to-ductile transition owing by the addition of COPUP. The crystallization behavior was studied by differential scanning calorimeter (DSC). The strain at break and notched impact strength of PLA/COPUP blends were increased more than 112–15.4 times elegant of neat PLA; the increase is superior to previous toughening effect by using petroleum-based tougheners. Furthermore, the thermal resistances and melt flow properties of the materials were also examined by analysis of the melt flow index and heat deflection temperature use in the work. With enhanced toughness, the PLA/COPUP blends could be used as replacements for some traditional petroleum-based polymeric materials.

Stiff Biodegradable Polylactide Composites with Ultrafine Cellulose Filler

Polylactide (PLA) composites with 10–30 wt% of commercial fine grain filler of native cellulose were prepared by melt-mixing, and examined. The composite films had esthetic appearance, glossy surface, creamy color and density close to that of neat PLA. Good dispersion of the filler in PLA matrix was achieved. The composites were stiffer than neat PLA; in the glassy region the storage modulus increased by approx. 30 %. The tensile strength of the composite materials in the temperature range from 25 to 45 °C was similar to that of neat PLA. No marked decrease in molar mass of PLA in the composites occurred during processing in comparison to neat PLA. Moreover, thermogravimetry experiments demonstrated good thermal stability of the composites; 5 % weight loss occurred well above 300 °C.

Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight

Blends containing 75 wt. % of an amorphous polylactide (PLA) with two different molecular weights and 25 wt. % of a poly[(butylene adipate)-co-terephthalate] (PBAT) were prepared using either a Brabender batch mixer or a twin-screw extruder. These compounds were selected because blending PLA with PBAT can overcome various drawbacks of PLA such as its brittleness and processability limitations. In this study, we investigated the effects of varying the molecular weight of the PLA matrix and of two different mixing processes on the blend morphology and, further, on droplet coalescence during shearing. The rheological properties of these blends were investigated and the interfacial properties were analyzed using the Palierne emulsion model. Droplet coalescence was investigated by applying shear flows of 0.05 and 0.20 s−1 at a fixed strain of 60. Subsequently, small amplitude oscillatory shear tests were conducted to investigate changes in the viscoelastic properties. The morphology of the blends was also examined using scanning electron microscope (SEM) micrographs. It was observed that the PBAT droplets were much smaller when twin-screw extrusion was used for the blend preparation. Shearing at 0.05 s−1 induced significant droplet coalescence in all blends, but coalescence and changes in the viscoelastic properties were much more pronounced for the PLA-PBAT blend based on a lower molecular weight PLA. The viscoelastic responses were also somehow affected by the thermal degradation of the PLA matrix during the experiments.

Electrical, mechanical and thermal properties of aligned silver nanowire/polylactide nanocomposite films

In this work, electrically conductive silver nanowire (Ag NW) filled polylactide (PLA) nanocomposites were fabricated and characterized. Ag NWs/PLA nanocomposite films were fabricated using simple solution mixing method and casted onto glass substrates via doctor blading. Following the obtainment of free standing nanocomposites through peeling off, electrical conductivity of the fabricated nanocomposites, interfacial interactions between Ag NWs and PLA as well as nanocomposite morphology, degree of alignment of Ag NWs, transition temperature and crystallinity among with mechanical performance were investigated. NWs showed good dispersion within the PLA matrix. Due to their high aspect ratio (≈150), a percolation threshold of 0.13 vol% was measured for the nanocomposites. Conductivity of the nanocomposites at the maximum loading (1.74 vol%) was measured as 27 S/m. It was also found that the transition temperatures of PLA matrix remain the same following the formation of nanocomposites. The results obtained herein revealed the potential of these nanocomposite films for electrostatic packaging and electromagnetic shielding applications.

Toughening effect of annealing-induced intermolecular crystallization of PBA-g-PLLA in PLA matrix

The intermolecular interaction between polylactide (PLA) and the impact modifier can generate high impact energy dissipation upon fracture. In this study graft copolymer impact modifiers that were composed of poly(n-butyl acrylate) (PBA) on the main chain and crystalline poly(L-lactide) (PLLA) on the side chain were prepared to investigate the intermolecular crystallization between the PLLA moiety and the PLA matrix. L-Lactide or D,L-lactide was graft copolymerized with PBA to yield either crystalline poly(n-butyl acrylate-g-L-lactide) (PBGL) or amorphous poly(n-butyl acrylate-g-D,L-lactide) (PBGDL). PBGL/PLA blend and PBGDL/PLA blend were prepared in the melt state, while the PBA content of each blend was fixed at 10 wt%. Annealing of the blends was performed at 100 oC for 4 h to modify the degree of crystallinity. The degree of crystallinity in all blends and neat PLA was increased by about 20% after annealing. The impact strength of the annealed PBGL/PLA blend was twice of that of the unannealed PBGL/PLA blend. However, the impact strengths of the PBGDL/PLA blend was not affected upon annealing, while annealing caused 10% reduction in impact strength of neat PLA and the PBA/PLA blend. The impact strength of the PBGL/PLA blend was found to be improved due to the intermolecular crystallization, resulting in expanded cavitation, debonding, shear yielding and fibrillar structure during fracturing.

Influences of three different ethylene copolymers on the toughness and other properties of polylactide

The aim of this study was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene-methyl-acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl-methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1–5 µm sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness and GIC fracture toughness values of PLA were as much as 160, 320 and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values.

Investigation on Polylactide (PLA)/Poly(butylene adipate-co-terephthalate) (PBAT)/Bark Flour of Plane Tree (PF) Eco-Composites.

Polylactide (PLA)/poly(butylene adipate-co-terephthalate) (PBAT)/bark flour of plane tree (PF) eco-composites were prepared via melt blending. The morphologies, mechanical properties, crystal structures and melting and crystallization behaviors of the eco-composites were investigated by means of scanning electron microscopy (SEM), mechanical tests, polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), respectively. It is shown that the interfacial adhesion between PLA matrix and PF is weak and the mechanical properties of PLA/PF eco-composites are poor. The titanate treatment improves the adhesion between the matrix and the filler and enhances the stiffness of the eco-composites. The toughness is improved by PBAT and ductile fractured surfaces can be found. The spherulitic size of PLA is decreased by the addition of PF. The α crystalline form of PLA remains in the composites. Compared with PF, T-PF (PF treated by a titanate coupling agent) and PBAT have negative effects on the crystallization of PLA.

Influence of Biodegradable Poly(butylene carbonate) on Plasticized Polylactide Blown Films

ABSTRACTThe polylactide (PLA) was blended with poly(1,2‐propylene glycol adipate) (PPA) and poly(butylene carbonate) (PBC). Then the extruded PLA/PPA/PBC blends were processed in the form of blown films. All of the ingredients used in the films are biodegradable. The miscibility, fracture surface morphology, and rheological properties of the PLA/PPA/PBC blends, further thermal properties, the tear‐fracture surface morphology, crystalline morphology, and mechanical and optical properties of the blown films were investigated. PPA did not enhance the miscibility between PLA and PBC. From SEM micrographs of the cryogenically fracture surfaces, PBC particles evenly dispersed in the PLA matrix. It could increase the nucleating density of the spherulites and decrease the size of the spherulites of PLA. The results indicated that the 85.5/9.5/5 PLA/PPA/PBC film had excellent tensile strength, elongation at break, tear strength, and transmittancy. The shear yielding induced by cavitation of PBC particles was the major tearing mechanism during the film tear test. The enzymatic degradation of PLA was slightly retarded in the presence of both PPA and PBC. These findings contribute new knowledge to the additives area and give important implications for manufacturing biodegradable polymer packaging materials.

Highly toughened polylactide with epoxidized polybutadiene by in-situ reactive compatibilization

Relatively high contents of rubber are commonly required to trigger the brittle-to-ductile transition when using rubber components to toughen polylactide (PLA). However, the strength may drop remarkably after incorporation of large amount of rubber. The main motivation of the present work is to achieve a good toughness-strength balance in a PLA/rubber system with less amount of rubber phase (90/10 w/w). In this study, polybutadiene (PB) was used to toughen PLA due to the flexible molecular chains. In attempt to enhance the compatibility of PB in PLA matrix, epoxidized polybutadiene (EPB) with different epoxidation degree were prepared by an in situ peroxy-formic acid method. The compatibility, phase morphologies, mechanical properties and thermal properties of the PLA/EPB blends were investigated respectively. It was found that epoxy group of EPB showed a significant effect in enhancing compatibility between rubber phase and PLA matrix, giving rise to a remarkable decrease in the particle diameter of rubber phase. When both of the good compatibility and the appropriate particle size of the rubber phase were realized, the impact toughness of PLA/EPB blend was improved by 13 times for that of pure PLA, while the tensile strength still preserved as a level of 77% (based on the value of pure PLA). The interfacial compatibilization between PLA and EPB was achieved through the formation of graft-copolymer being a compatibilizer caused by the in-situ reaction between EPB and PLA in the melt blend process. This result proves the introduction of active groups into PLA blends to be a platform to design their performance via regulating the phase structure.

Shear rheology of polylactide (PLA)–cellulose nanocrystal (CNC) nanocomposites

A simple method for the preparation of polymer-cellulose nanocrystal (CNC) nanocomposite is shown to yield good dispersion of CNCs within a polylactide (PLA) matrix, which consequently resulted in the lowest rheological percolation threshold reported so far for polymer-CNC systems. The rheological behavior of the nanocomposites was determined in dynamic, transient, and steady-shear flow fields in the molten state. The complex viscosity and storage modulus of the nanocomposites increased markedly with CNC content, particularly at low frequencies; the samples were highly shear thinning and exhibited a transition from liquid- to solid-like behavior as the CNC concentration increased. Larger values for steady-state viscosity, yield stress, shear stress, and first normal stress difference were reported for the more concentrated nanocomposites. Also, pronounced overshoots in the transient start-up viscosity of the nanocomposites were observed. These results could be ascribed to the formation of an interconnected CNC network within the PLA matrix.

Simultaneously reinforcing and toughening of polylactide/carbon fiber composites via adding small amount of soft poly(ether)urethane

Bio-degradable polylactide (PLA) based composites has attracted much attention both in academic research and industrial applications in recent decades due to the increasing environmental concerns. In this work, we tried to obtain PLA based composites with good stiffness-toughness balanced properties by adjusting carbon fiber (CF) network in polylactide (PLA) matrix via adding a small amount of soft poly(ether)urethane (PU). It was interesting to find that PU could serve as “solder” to weld CF into a more perfect network due to the fact that PU has stronger interaction with CF as compared with PLA and improve the interface interaction between CF and PLA meanwhile. The self-weld CF network structure was confirmed by SEM characterizations, rheology and conductivity tests. More importantly, the formation of self-weld network structure constructed by both stiff CF and ductile PU elastomer can simultaneously improve tensile strength, impact toughness and even electrical conductivity of PLA. This inspiring result demonstrates that the addition of soft elastomer which has a strong interaction with fiber into fiber-reinforced polymers could be a universal platform to improve the performance of polymer composites via tuning fibers network and the interfacial interaction between fibers and polymer matrix.

Supermolecular structure and nucleation ability of polylactide-based composites with silica/lignin hybrid fillers

In this paper, amorphous silica Syloid 244 and kraft lignin were mechanically coupled. Four hybrid materials containing silica and lignin in ratios 1:1, 2:1, 5:1 and 20:1 were prepared. As reference samples for hybrid fillers pristine silica and lignin were used. Particle size determination and microscopic observations were applied to determine dispersive and morphological properties of hybrid fillers. Fourier transform infrared spectroscopy confirmed the effective preparation of silica/lignin hybrid materials. The parameters of porous structure of examined hybrid filler were determined using the multipoint Brunauer–Emmett–Teller method and Barrett–Joyner–Halenda algorithm. Composite samples of polylactide (PLA) containing 2.5 % (w/w) of hybrid filler were extruded. Optical microscopy, wide-angle X-ray scattering and differential scanning calorimetry were applied to specify the supermolecular structure of functional PLA/hybrid composites and analyze the crystallization parameters as well as the phase transformation in PLA matrix. Silica/lignin hybrid material was found to be a filler capable of an effective crystal nucleation. The nucleating ability of silica/lignin hybrid filler in PLA matrix is related to porous properties of filler and its composition.

An Ultraviolet-Induced Reactive Extrusion To Control Chain Scission and Long-Chain Branching Reactions of Polylactide

Free-radical reactions of polymers, including biodegradable polymers via reactive extrusion, are normally induced by peroxide chemicals, which are known to lead to the formation of secondary products and impart some performances to the resin. Here, we report an ultraviolet (UV)-induced reactive extrusion, without employing a peroxide initiator, to control chain scission and branching reactions of polylactide (PLA). Through this technique, chain scission reaction of molten PLA induced by UV irradiation during extrusion was promoted to high-level efficiency. Degraded PLA samples had lower complex viscosity and storage modulus, because of random main chain scissions. Long-chain branched (LCB) structure of PLA was obtained when a multifunctional chemical agent, trimethylolpropane triacrylate (TMPTA), was added into the PLA matrix during extrusion. Various rheological plots including viscosity, storage modulus, loss tangent, and Cole–Cole plots were used to distinguish the LCB structures of PLA samples. Therma...

Dynamic vulcanization of castor oil in a polylactide matrix for toughening

Dynamic vulcanization of biomass-derived castor oil in the presence of 4,4′-diphenylmethane diisocyanate (MDI) in a polylactide (PLA) matrix was performed with the aim of toughening PLA sustainably.

Influence of reprocessing on fibre length distribution, tensile strength and impact strength of injection moulded cellulose fibre-reinforced polylactide (PLA) composites

The present study focuses on the reprocessing behaviour of recycled injection moulded polylactide (PLA) composites. The composites are reinforced with regenerated cellulose fibres (lyocell) of variable fineness and a fibre mass content of 30%. They were reprocessed up to three times. The influence of reprocessing on the fibre length distribution and the resulting composite mechanical properties (tensile and impact strength) was analysed. While the first reprocessing cycle does not affect the mechanical characteristics of the neat PLA matrix, the strength of the composites decreases significantly due to a decreasing fibre aspect ratio. It was shown that fibres having a larger cross-sectional area display a lower aspect ratio than finer fibres, after reprocessing. This phenomenon leads to a larger decrease in tensile strength of composites reinforced with coarser fibres when compared to composites reinforced with finer fibres. A comparison of virgin composites and threefold reprocessed composites with a similar fibre length distribution resulted in a significantly higher tensile strength compared to the virgin sample. This result leads to the conclusion that not only the fibre length is drastically reduced by reprocessing but also that the fibres and the matrix were damaged.